The present invention pertains to a device and a method for the precipitation of dust which is created in particular during the manufacture of a crystal grown from a melt and which can be added as a dust mixture to a transport gas for diverting it from the melt chamber.
In the growth of crystals from a melt, such as in the Czochralski or Bridgeman method, or other methods for melting or remelting the starting crystalline material, the melting process takes place within processing chambers separated from the external atmosphere. In this case, the melt is held in a crucible which is located inside an evacuated vessel. Depending on the vapor pressure and the temperature of the molten material, a vapor cloud composed of the molten material forms above the melt crucible. This cloud contains particles which have diameters of less than one micrometer and which tend to agglomerate into larger particles of dust. Sufficiently large dust particles can then drop back into the melt, so that the crystallization process is disrupted, and consequently, the growth of the monocrystal must be interrupted.
In order to prevent the disruption caused by the dust, the dust particles are usually removed from the process chamber by means of a continuous gas stream. The gas used in this case is introduced through a gas inlet into the processing chamber, directed over the opening of the melt crucible, and is then vacuumed off together with the collected dust by a vacuum pump and output through an exhaust opening. Due to the highly abrasive nature of the pumped dust, which may consist of SiO, for example, in the growth of Si-monocrystals, the dust is usually filtered out in dust filters connected in series with the vacuum pumps. In this regard, these filters have porous surfaces to separate and collect the dust.
One problem in the use of these known filters is that their capacity for collecting dust is quickly reached when dust generation is heavy, even when they are generously proportioned with respect to the total generated quantity of dust, and these porous surfaces must then be replaced with new ones. Usually either the entire filter arrangement must be shut down to remove the filter and the gas stream must be shunted through a second, separate filter arrangement, or the filter must be designed for the maximum quantity of dust likely to be encountered. Both alternatives are less than optimal from a design standpoint and are associated with added expense. Moreover, the manual handling of these dust-laden filter elements is associated with health risks, which, in turn, can only be avoided by additional apparatus expense.
Therefore it is an object of the present invention to enable the cleaning and purification of scavenging gas used in the growth of crystals, which is easy to implement and economical to apply.
It is a further object of the present invention to provide a suitable filter apparatus to remove the dust admixed into the scavenging gas, that has a high capacity, that is easy to produce in a simple manner, and that also allows simple handling.